1. Field of the Invention
The present invention relates to a process for producing a polyolefin. More particularly, it relates to a process for producing a polyolefin by two step polymerization under a specific condition in the presence of a specific catalyst and a cocatalyst to impart excellent extruding property, excellent stability in an inflation process of a tubular product, excellent texture, impact strength and environmental stress crack resistance of a film and excellent strength of an inflation molded film and less formation of fisheye.
2. Description of the Prior Art
In general, polyethylene is molded into a film by an inflation process or T-die process etc. Recently, the speed for molding has been fastened because of an improvement of a molding machine and an improvement of productivity. When the speed for molding is fastened especially in an inflation process, the molten polymer extruded becomes unstable not to produce a tubular product in stable and an uniform film is not easily obtained and an appearance of the film is sometimes inferior.
In order to obtain a tubular product in stable, it has been considered to incorporate a radical initiator. When a content of the radical initiator is too much, the strength of the film is inferior to cause a gel or spots and the range for the balance of the stability of the tubular product and the strength of the film are narrow.
The inventors have studied processes for producing a polyolefin which has excellent moldability especially extrusion property and stability of a tubular product in an inflation process, excellent texture of a film and has excellent impact strength and environmental stress crack resistance, high strength of an inflation molded film and less fisheye.